Rim anchoring systems for flexible surgical implants for replacing cartilage

ABSTRACT

Flexible cartilage-replacing implants are disclosed that use either or both of ( 1 ) enlarged peripheral rim components, and/or ( 2 ) elongated flexible reinforcing members that are embedded around the peripheral edge of an implant device. These types of anchoring devices, especially when used in combination, can provide flexible implants that can be implanted arthroscopically into synovial joints, for complete replacement of damaged cartilage segments.

RELATED APPLICATION

This application is a continuation-in-part of U.S. utility applicationSer. No. 13/355,276, which in turn claimed priority, under 35 USC 119,based on provisional application 61/434,145, filed on Jan. 19, 2011.

BACKGROUND OF THE INVENTION

This invention is in the field of surgical implants, and relates todevices and methods for repairing hyaline or meniscal cartilage injoints such as knees, hips, fingers, shoulders, etc.

In joints that are lubricated by synovial fluid, hyaline and meniscalcartilage segments provide smooth, slippery, lubricated (or lubricious)surfaces that enable bones to move and slide, relative to other bones.“Hyaline” cartilage refers to the types of cartilage segments that areaffixed, in relatively thin layers, directly to bone surfaces (oftencalled condyles). Background information on hyaline cartilage, and onsurgical implants for replacing injured or diseased hyaline cartilage,is available from various sources, including several prior patentapplications by the same inventor herein, such as Ser. Nos. 11/390,539(“Implants for replacing hyaline cartilage, with hydrogel reinforced bythree-dimensional fiber arrays”), 11/105,677 (“Hydrogel implants forreplacing hyaline cartilage, with charged surfaces and improvedanchoring”), and 10/071,930 (“Cartilage repair implant with soft bearingsurface and flexible anchoring device”).

Meniscal cartilage is more complex. Each knee joint has two meniscalsegments, which are arc-shaped segments with triangular cross-sections,depicted in any textbook on anatomy. These meniscal segments arepositioned on the left and right sides of each knee (referred to byphysicians as the “medial” (inside) and “lateral” (outside) positions,and they help stabilize the femoral runners against “sideways” motion.Each meniscal wedge has two smooth and lubricious surfaces (a smoothlower surface, which is roughly horizontal, and a smooth upper surface,which is slanted and which curves sharply around the interior curvedupper surface of the rounded wedge-type segment). These meniscal wedgesare made of a specialized type of “fibrocartilage”; rather than beingaffixed, like a thin coating layer, on a bone surface they haveanchoring ligaments, both at their tips (which attach to boneprotrusions near the center of a tibial plateau), and around theirperipheral surfaces (to the tendons and ligaments that form a “capsule”which encloses the knee and holds in the synovial fluid which lubricatesthe joint). Additional information on meniscal cartilage (as usedherein, that term includes a structurally similar set of “labral”cartilage segments in hip and shoulder joints), and on the design ofimplants for replacing or repairing damaged meniscal or labral cartilagesegments, is available from sources such as U.S. patent application Ser.No. 11/471,090, “Multi-part implants for combined repair of hyaline andmeniscal cartilage in joints”.

Joints that contain hyaline and/or meniscal cartilage (which includeslabral cartilage) are referred to herein as “synovial” joints, sincethey are lubricated by synovial fluid. These joints can alternately becalled “articulating” joints, because they involve joints having bonesurfaces which move, relative to each other, in a manner referred to as“articulating” motion. The types of cartilage (and joints) of interestherein specifically exclude: (1) cartilage in spinal discs, which do nothave any sliding surfaces, and which have a very different structure andbone-anchoring system, which actively prevents any sliding or shearingmotions, since any such motion could severely injure the spinal cord;and, (2) other non-sliding, “non-articulating” cartilage, which ispresent in various body parts such as the nose, ears, windpipe, etc.Neither of those two types of cartilage (in spinal discs, or in ears,noses, windpipes, etc., not need to withstand the types of loadings andstresses that are imposed on synovial (i.e., articulating) joints.Therefore, implants which are designed to replace cartilage in spinaldiscs, or in ears, noses, windpipes, etc., do not require the types ofspecialized anchoring systems disclosed herein.

All implants of interest herein are specifically designed to be“substantially flexible”, to a point which will enable “minimallyinvasive” surgical implantation, since flexibility can enable an implantdevice to be at least partially curled or rolled up, compressed, orotherwise flexed into a shape that can pass through a smaller incisionthan would be required by a non-flexible implant. Anything that canminimize the amount of cutting and disruption of soft tissues andvasculature, in and around a joint that is being repaired, will minimizedamage to the surrounding tissues, thereby benefiting the patient andreducing pain, recovery times, risks of infection, etc.

The optimal type of minimally-invasive surgery on joints is arthroscopicsurgery, in which all necessary instruments and devices enter a jointvia small slits. In this type of surgery, any implant devices should bedesigned to allow passage through an arthroscopic insertion tube havingthe smallest practical diameter. Accordingly, the implants describedherein preferably should be not merely slightly flexible; instead, anoptimal implant should be flexible enough to be rolled up into acylindrical configuration, to allow an implant to be inserted into ajoint via an arthroscopic insertion tube.

If not adequately defined, the term “flexible” is inherently indefinite;for example, it can be argued that virtually anything that is notbrittle or friable is (or can become) flexible, if enough force isapplied. Therefore, a set of practical limits and “benchmark” standardsis established and used herein, to define “flexible” (as that term isused in the claims), and to determine whether some particular implanthas sufficient flexibility, on a practical level, to render it suitedfor use as disclosed herein.

Accordingly, a candidate implant device is deemed to be “flexible”, asused in the claims, if the device (as manufactured and assembled in aform that will be removed from a sealed sterile envelope by a surgeon,immediately before implantation during a surgical procedure), meetseither or both of the two following criteria:

(1) if it can be flexed (or curled, rolled, bent, etc.), withoutrequiring tools, into a configuration that has an “angle ofdisplacement” of at least about 70 degrees. By way of illustration, ifone edge of the implant is held horizontal, on the surface of a table,the opposing edge must be capable of being lifted to an angle of atleast 70 degrees from horizontal, which is equal to 20 degrees short ofcompletely vertical.

(1) if it can be flexed, without requiring tools, into a configurationwhere its “width” (i.e., its smallest dimension, when looked at from a“top view” or “plan view”) is reduced to about 80% or less of its widthin a non-flexed, relaxed state. By way of illustration, if a femoralrunner or a meniscal wedge can be temporarily “straightened out”, from acurved and relatively semi-circular shape into a more linear shape thatcan be pushed into a joint via an insertion slit or tube, it can enablethe insertion of the femoral or meniscal implant into a joint, with lessdamage to surrounding tissues.

If an implant as described herein is designed for replacing hyalinecartilage (which is relatively thin), it preferably should surpass thoseminimum levels of flexibility, and the implant should be capable ofbeing rolled into a cylindrical configuration, for implantation via anarthroscopic insertion tube.

Shape-Memory and Super-Elastic Materials, and Nitinol

Since high levels of flexibility will be required for arthroscopic useof the implants disclosed herein, three specific terms of art in thefield of materials science should be introduced and briefly explained.These three terms are shape-memory materials, super-elastic materials,and nitinol.

In general, “shape-memory materials” (SMM's, which includes variouspolymers as well as certain types of alloys) include any materials thatfall within either of two somewhat different functional definitions.

Under the first definition, if a material can be deformed (such as bybending, stretching, etc.) in some way that appears to be stable, undersome particular set of conditions, but if the material will return toits manufactured shape without suffering any permanent damage, whensubjected to different conditions, then the material is classified as a“shape-memory material”. A common parameter that is used to manipulateshape-memory materials, in ways that make convenient and valuable use oftheir “shape-memory” trait, is temperature.

For lack of a better descriptive term, the phrase “shape-memorymaterials” also acquired a second functional definition. If a certainalloy or polymer undergoes some type of “phase transition” which leadsto a notably different type of physical performance or behavior, whensubjected to a certain type of operating condition or parameter, andthen it returns to its “normal” performance or behavior when returned to“normal” conditions, the term “shape-memory material” is often used as alabel for that type of material, regardless of whether the differentperformance actually involves shape. This convention apparently arosewhen it was discovered, during the 1930's, that wires made of certaintypes of copper-zinc alloys would shrink, in length (which is indeed achange in shape), when heated; these types of wires came to be used inrobotics and toys, as “muscle wires” that would contract, in length,when a current was applied to such wires in a way that caused heating ofsuch wires.

A subsequent development that became of major medical importance arosewhen it was discovered, in the 1960's, that certain types of alloyscontaining nickel and titanium had an unusual behavior. Those alloyswere called “nitinol” alloys (pronounced NIGHT-in-all), as a splicedacronym that combines the first letters from nickel, titanium, and“Naval Ordnance Laboratories”, the federal research center where nitinolalloys were discovered. Nitinol alloys undergo a temperature-dependenttransition that is the opposite of what occurs in most types of alloysand polymers. Most non-rigid alloys and polymers tend to become softer,and more flexible and pliable, when they are heated to highertemperatures. Nitinol alloys become of interest in medical devices,because they can do the exact opposite. At normal human bodytemperatures, nitinol alloys are in an “Austenite” crystalline form,which is relatively stiff. However, if a nitinol device is chilled incold water (such as saline slush), it makes an entirely reversibletransition to a “Martensite” crystalline form, which is substantiallymore flexible and pliable.

As a result of that unusual behavior, various types of medical devicesare made of nitinol, such as stents (devices for holding blood vesselsopen, in people who suffer from partially blocked or occluded arteriessuch as in the heart or neck). These can be implanted and used asfollows. If a stent, made of nitinol in the form of a cylindrical wiremesh, is chilled to a “Martensite” temperature (such as by immersing itin cold water), the stent can be compressed into a relatively smalldiameter that will fit inside a catheter tube, which can be “snaked”into a patient's body via a small incision, such as into a femoralartery. The stent can be kept chilled, while it remains in the cathetertube, by using cold water circulating through special channels in thecatheter. After the stent reaches a blood vessel that needs to beunclogged, the catheter tube is withdrawn, allowing blood andsurrounding tissues to warm the stent back up to its stiffer “Austenite”state. As that warming process occurs, the stent will expand back intoits larger, unstressed, manufactured diameter, which will correspond tothe inside diameter of the artery segment that needs to be kept open.

These types of nitinol devices, and the transitions they undergo atdiffering temperatures, are described and shown in more detail innumerous sources, including a website (www.nitinol.info) run by acompany called Nitinol Devices and Components (NDC). Several shortvideos (about 1 minute each), which visually depict how nitinol alloysand devices behave, are available atwww.nitinol.info\pages\technology.html. In addition, a review article byD. Stoeckel, “Nitinol Medical Devices and Implants”, presented at theSMST 2000 Conference, is available atwww.nitinol.info/pdf_files/stoeckel_(—)1.pdf.

Accordingly, nitinol devices will not make self-directed transitionsinto shorter or longer lengths, or other different shapes, when chilledor heated. However, since they become more pliable and “workable” whenchilled, they can be readily manipulated into useful shapes (for animplantation process or other purpose) at cold temperatures, and theywill then return to a stiffer and stronger manufactured state andgeometry, when allowed to warm up to body temperature. As a result, theyare usually included within the class of materials called “shape-memorymaterials”.

The term “super-elastic material” is broader, and it does not have aprecise definition. As implied by the term “super”, it includesmaterials with one or more elastic behaviors that would be regarded assuper or superb (which implies especially useful, valuable, and somehowdifferent and better), when compared to conventional elastic materials.In the field of metals, conventional elasticity can be represented andexemplified by long, thin, flexible pieces of stainless steel, or by thetypes of steel alloys used to make metal springs. In plastics andpolymers, conventional elasticity is represented by latex rubber,silicon rubber, rubber bands, etc. Accordingly, “super-elasticmaterials” include materials that can substantially outperform thosetypes of conventional materials, in one or more ways that involveelasticity. Since “shape-memory materials” that respond to temperaturechanges, and “muscle wires” that become either shorter or longer whenelectric currents are passed through them, both fall within thatdefinition, those are often referred to as types of super-elasticmaterials.

One other point should be noted. In nearly all cases of interest herein,a device made from a shape-memory material usually will seek to returnto a certain shape (which will be determined by the manufacturingprocess), when it returns to a “final” temperature (which will be bodytemperature, for any surgical implant) or other operating condition.This distinguishes shape-memory devices from items such as rubber bands.A rubber band is elastic, and it will return to a certain length, afterany tension that caused it to take an elongated shape has been removed.However, a typical rubber band that has a substantial length will notattempt to return to a certain specific shape. If dropped onto a flatsurface, it can come to rest in a relatively straight or oval-likeconfiguration, or it can curve in either a right or left direction,without any substantial stresses arising within the rubber that makesthe rubber band.

By contrast, in all cases of interest herein, a shape-memory device willhave a predetermined shape, which must be created during a manufacturingoperation (which can include various annealing, curing, treating, orother shape-imparting or shape-modifying steps). The device will thenseek to return to that predetermined shape. This does not imply that thedevice must and will always return to exactly its manufactured shape;nevertheless, it will seek to do so, and any shape alterations that maybe imposed on the device, by external mechanisms or forces (such asanchoring pins, an adhesive that is used to bond the material to anothersurface, etc.), will create some level of internal stresses within theshape-memory or super-elastic device.

Accordingly, proper design of a surgical implant made of a shape-memoryor super-elastic material must take into account the final shape thatthe device will take, after it has been implanted in a particularlocation. Some implants are intended to impose mechanical forces on bodyparts or mechanical components that contact an implant; this iscomparable to installing a spring-loaded device inside a mechanism.However, if creating that type of force is not the intent of ashape-memory or super-elastic implant device, then the implant should bemanufactured with an unstressed shape that is as close as possible tothe final shape the implant will take, after it has been implanted.

That is a brief introduction to a complex field of materials science.Much more information on these types of materials is available in bookssuch as Otsuka and Wayman, editors, Shape Memory Materials (CambridgeUniv. Press, 1999), and from an organization called Shape Memory andSuperelastic Technologies (SMST), www.smst.org. A surgeon does not needto be an expert in this field of materials science, in order to be ableto use and appreciate surgical devices that incorporate and use thesetypes of materials. If a surgeon has a working knowledge of what thesematerials and devices can accomplish, and how they will perform whenused in surgical implants, that is sufficient.

Returning to the subject of nitinol alloys, it was initially believed,by the Applicant herein, that certain types of rims or other anchoringcomponents made of nitinol alloys would be ideal, forcartilage-replacing implants, because the use of nitinol alloys wouldallow them to become much more soft and flexible, by using a chillingprocess, during insertion into a joint that is being surgicallyrepaired. However, additional research by the Applicant has identifiedan important obstacle to such use of nitinol alloys, in implants thatwill remain in a patient's body for an extended period of time. Thatobstacle involves a risk of corrosion, which is believed to ariseprimarily in areas where nickel atoms cluster together in“nickel-enriched” clusters or “pockets” that can have molecularstructures and/or “lattice ratios” such as Ni3Ti. The bonds betweenadjacent nickel atoms are not as strong as the bonds between nickel andtitanium atoms. As a result, during the manufacture of a nitinolcomponent, if small pockets of material are formed that have nickelcontent greater than 50%, the nickel atoms in those pockets can beleached out, over a span of months or years, in ways that can lead tocorrosion, cavities, and structural weakness.

It has been discovered, through testing, that a nitinol manufacturingprocess known as “Quick Cool with No Reheat” provides morecorrosion-resistant nitinol alloys than a different process known as“Cool Down Slowly”. Accordingly, nitinol alloys have been approved foruse in some medical devices that are left in place for years, such ascertain types of stents that help keep arteries open in patients whosuffer from clogged arteries.

However, since the types of arthroscopically-insertable flexibleimplants being developed by the Applicant herein, for orthopedic use inload-bearing joints such as hips or knees (where any such implants willneed to comply with stricter design requirements and constraints,compared to uses in non-load-bearing locations, such as stents) alreadyhave a number of novel and even pioneering features, when compared toconventional orthopedic implants that are in use today (as exemplifiedby conventional “total knee replacement” implants), this new andinnovative “technology platform” is not well-suited for introducing newcomponent and material selections that might trigger extensiveadditional long-term clinical testing requirements. Those types oflong-term testing requirements could lead to severe problems and delays,especially if the main goal of such long-term clinical trials would beto ensure that a certain type of component material will not slowlycorrode, over a span of a decade or more, in a mammalian joint.

Therefore, the Applicant herein began studying alternate types ofcandidate reinforcing devices, using materials that have long trackrecords of biocompatibility with biological fluids and tissues, andwhich do not pose any risks or questions of potential slow and gradualcorrosion. The results of those efforts are described below, as part ofthis invention.

However, it also should be noted that the use of nitinol, incartilage-replacing implants designed for permanent implantation (inthis context, phrases such as “long term” generally refer to timeperiods greater than at least 5 or 10 years, while “permanent” refers tothe remaining life of a patient), might remain as a completely viableapproach, if any such nitinol component will be completely embeddedwithin a polymeric material that will effectively “seal in” (or entomb,or similar terms) the nitinol component, in a way that will prevent anynitinol from ever being contacted, in any significant quantities, bybody fluids. That is indeed the design of various types of implantsdescribed and illustrated herein; accordingly, the use of nitinolanchoring rims, in such devices, remains as a potentially feasible,practical, and approvable design approach, in such implants.

Accordingly, one object of this invention is to disclose improveddesigns and constructions for flexible surgical implants that aredesigned and suited for arthroscopic repair and replacement of hyalineand/or meniscal cartilage, in synovial joints.

Another object of this invention is to disclose improved devices,assemblies, and methods for anchoring, to bone surfaces in synovialjoints, flexible surgical implants which are designed for arthroscopicrepair and replacement of hyaline cartilage.

Another object of this invention is to disclose improved devices,assemblies, and methods for anchoring flexible surgical implantsdesigned for arthroscopic repair and replacement of damaged meniscal orlabral cartilage.

These and other objects of the invention will be become more apparentthrough the following summary, drawings, and detailed description.

SUMMARY OF THE INVENTION

Improved designs are disclosed for flexible implants that will be usedto surgically replace hyaline or meniscal cartilage, in synovial joints.In one preferred embodiment, a hydrophilic polymer, molded generally inthe shape of a damaged cartilage segment that needs to be replaced, willhave an enlarged peripheral rim that is substantially thicker than theinterior portions of the implant. That enlarged peripheral rim will bedesigned to fit, in an accommodating manner, into a “groove” that willbe machined (with the help of templates, computerized tools, etc.) intothe bone surface that will receive and support the implant. This willcreate an interlocking-type “fit” that will provide greater strength andstability for the implant, to allow it to resist shear forces evenduring a fall, accident, or other moment of “peak loading” or peakstress.

If desired, a “stabilizing ring”, which can be made of a shape-memoryand/or super-elastic material (such as a “nitinol”-type alloy, ifdesired), or alternately from a braided or twisted multi-strand wire,cable, or similar component, can be embedded within the peripheral rimof the polymer component. This can allow the implant to be flexed into acylindrical or other elongated, compressed, or other shape, forminimally-invasive insertion into a joint (such as via an arthroscopicinsertion tube). After the implant has entered the joint, it will emergefrom the insertion tube, or otherwise will be allowed or caused toreturn to its normal shape. This will enable the implant, with itsenlarged outer rim containing a “stabilizing ring” component embeddedwithin that rim, to perform a reinforcing and stabilizing role when theenlarged and reinforced flexible polymer rim of the implant settles intothe bone groove.

The stabilizing ring also can be provided with means for securing theimplant to anchoring components (such as bone screws) that can beemplaced before the implant is inserted into the joint. Alternately oradditionally, the periphery of the implant can be provided with otheranchoring means, either directly or indirectly, such as suture strands,cerclage wires, reinforcing mesh extensions, or other devices having“free ends” that can be secured to bone or soft tissue by variousconventional means (including staples, sutures, screws, etc.), or by thetypes of ratcheting suture anchors which are described in more detail inrelated application Ser. No. 13/355,276 by the same Applicant herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the upper (or exposed, or articulating)surface of a surgical implant for replacing hyaline cartilage, showing aflexible polymer component with a smooth and lubricious articulatingsurface, and also partially showing anchoring screws on the underside(or anchoring surface) of the implant.

FIG. 2 is perspective cutaway view of the surgical implant, showing aflexible stabilizing ring (which can be made of a shape-memory orsuper-elastic material) that is embedded within an enlarged peripheralrim made of a flexible synthetic polymer. Screw-holder caps (which willsnap onto the heads of anchoring screws, after the screws have beenemplaced in a supporting bone surface) are affixed to the stabilizingring, at spaced locations around the periphery of the implant.

FIG. 3 is a perspective view of the anchoring surface (or underside, orsimilar terms) of the surgical implant shown in FIG. 2.

FIG. 4 is a perspective view of an anchoring screw, with a rounded “snapcap” head, and with a “shoulder ring” affixed to the neck of the screw,which will press against a stabilizing washer that will press against abone surface.

FIG. 5 is a perspective view of screw-holder cap, affixed to astabilizing ring of an implant, which has been pressed and “snapped”onto the rounded head of an anchoring screw.

FIG. 6 is a cutaway side view depicting an anchoring component, in theshape of a large “washer” with an open center, which is securely affixedto a supporting bone by means of screws, pins, cement, etc. After that“anchoring washer” has been securely affixed to the bone, a flexiblepolymer implant is inserted into the joint, and the enlarged rim of theimplant is pressed and nestled into a groove or trench that has beenmachined into the supporting bone surface. A circular ring, affixed tothe anchoring washer, will cause the flexible polymer implant to “snap”into the groove or trench in the bone surface, and will thereafterprevent dislodgement of the flexible implant. For clarity, FIG. 6illustrates only the anchoring system, and the central polymer componentof the flexible implant is not shown. The enlarged rim of the flexibleimplant contains a reinforcing component having a non-flatcross-sectional shape, modeled after a metallic tape-measure that can beextended in stiffened form, and retracted into a compact roll. Thisshape can allow the reinforcing component to undergo a “collapsibletransition” while it is being inserted into a joint; then, when theimplant and rim return to their relaxed manufactured shape, thereinforcing component will again become stiffer and stronger.

FIG. 7 is a perspective view with a partial cutaway section of aflexible implant, where the rim of the molded polymer component containsan embedded anchoring cable that is moderately stiff yet flexible.Anchoring pegs, which will engage anchoring sleeves that can be emplacedin a bone surface before the implant is inserted into a joint, arecoupled to the anchoring cable at spaced locations.

FIG. 8 is a perspective view of a cartilage-replacing implant, having aperipheral anchoring cable made of a stiff but flexible cable, embeddedwithin a flexible polymer component that has an enlarged rim, designedto fit into an accommodating groove or trench that has been machinedinto the supporting bone surface. Several “snap caps” are affixed to theanchoring cable, at spaced locations. These caps will attach to therounded heads of bone screws, which will be set in a bone surface beforethe implant is inserted into a joint.

FIG. 9 depicts a type of suture anchor having a crimping mechanism whichprovides the suture anchor with a ratchet-type control mechanism.

FIG. 10 depicts the same ratchet-type suture anchor shown in FIG. 9,after it has been bent and crimped in a manner that prevents looseningof the suture strand which pases through the anchor.

FIG. 11 is a cutaway view, showing upper and lower flexible anchoringcables embedded within a polymer segment having the size and shape of ameniscal wedge. A suture strand is shown wrapped around one cable, withboth ends of the suture strand emerging from the polymer segment; thisallows the ends of the suture strand to be used to anchor the peripheralsurface of the meniscal implant, to the soft tissues that form the kneecapsule. The ends of the anchoring cables are designed to be affixed tothe tibial plateau, in a manner and location that emulates the anchoringof natural meniscal segments.

DETAILED DESCRIPTION

As briefly summarized above, a surgical implant 100, designed forreplacing a relatively large segment of hyaline cartilage in a synovialjoint such as a knee, shoulder, hip, etc.) is illustrated in FIGS. 1-3.Scaled-down implants with the same structures described herein, but withsmaller diameters and thicknesses (and with only one or two anchoringscrews, pins, or other components, which also can be smaller) also canbe created for replacing hyaline cartilage in smaller joints, such as inthumbs, fingers, wrists, etc.

For simplicity of illustration, implant 100 is shown as having agenerally round and flat shape. In actual use, any such implant designedfor a large joint should have a molded and shaped articulating surfacethat will closely emulate the size and shape of the cartilage segmentthat is being replaced by the implant. The sizes and shapes of suchcartilage surfaces (such as, within a knee joint, the medial and lateralfemoral runners, the tibial plateau, and the patella (kneecap)), are allwell-known to orthopedic surgeons. Such implants can be manufactured inan assortment of sizes and shapes, and a surgeon who is repairing ajoint will select one or more implants having optimal sizes and shapesfor a specific patient, based on X-rays or similar images ormeasurements of the joint that will need to be repaired.

On that subject, it should be noted that the irregular surface of adiseased, injured, or otherwise damaged or defective cartilage segmentin any load-bearing joint typically will abrade and damage any othercartilage segment(s) that rub against the damaged and iregular surface;therefore, most such repairs will require at least two implant devices.For example, if a femoral runner needs to be replaced, then the portionof the tibial plateau which rubs and slides against the damaged femoralrunner will likely also need to be replaced. This is conventionalpractice in this type of orthopedic surgery, and the implant devicesdescribed herein will be well-suited for such use, if manufactured in arange and assortment of sizes and shapes that will allow a surgeon toselect suitably-sized implants based on the size, weight, and needs ofany specific patient.

Returning to FIGS. 1-3, the polymer component 110 of an implant 100preferably should be made of a single molded component to avoid andeliminate any surface seams (which can also be referred to as junctures,junctions, fissures, etc.) which otherwise might become potential weakspots, focal points for stress, and/or sites or sources of abrasion.Polymer component 110 comprises an enlarged peripheral rim 112 (shown incross-section in FIG. 2), a smooth and lubricious articulating surface114 (which will be coated and lubricated by natural synovial fluid,after implantation into a mammalian joint), and an underside oranchoring surface 116 (shown in FIG. 3). Any directional terms usedherein (such as up, down, top, bottom, above, under, etc.) assume that abone surface provides a horizontal “floor” (or base, support,foundation, etc.) for an implant, and the implant will rest on top ofthat horizontal base, with the anchoring surface (underside) of theimplant resting upon the supporting bone surface, and with thearticulating surface (which might can be called the “exposed” side ofthe implant) facing upward, on the “top” surface of the bone.

The types of polymers of interest herein can be manufactured by any ofseveral molding methods that are known to those skilled in the art,using a flexible but tough and durable hydrophilic polymer, such as asuitable hydrophilic polyacrylonitrile (PAN) or polyurethane. As knownto those skilled in polymer chemistry, terms such as polyacrylonitrileand polyurethane refer to the types of chemical linkages that are usedto create the long “backbone” chains within such polymer molecules. Anyof numerous types or combinations of “side groups” (also calledmoieties, pendant groups, and various other terms) and/or reactivecrosslinking groups can be chemically bonded to the backbone chains.This is usually done by proper selection of the “monomer” reagents thatare used to create a polymer; when monomer “links” are bonded to eachother to form the long “backbone” chains in a polymer, the side groupsthat were present in the monomers will become pendant groups attached tothe long backbone chains of the polymer. Accordingly, a polymer moleculewhich falls within a certain category or label (such aspolyacrylonitrile, polyurethane, etc., as determined by the types oflinkages in the long “backbone” chains) can be created with nearly anydesired types of side (pendant) groups, which will impart a set ofdesired traits to the final polymer. It will be the side groups thatwill control whether a polyacrylonitrile, polyurethane, or similarpolymer will be hydrophobic or hydrophilic, flexible or rigid, permeableor impermeable to water molecules, etc.

If desired, the exposed articulating surface of an implant of this typecan be given a controllable negative electrical (ionic) charge, by meanssuch as contacting the articulating surface for a controlled period oftime with dilute sulfuric acid, as described in published U.S. patentapplication Ser. No. 11/105,677, entitled, “Hydrogel implants forreplacing hyaline cartilage, with charged surfaces and improvedanchoring”. This type of treatment can create a polymer surface thatclosely emulates the negative charge density of natural cartilage, whichin turn will improve certain chemical interactions between the implantsurface, and certain types of positively-charged components of synovialfluid.

The entire polymer component 110 (or any portion thereof) of an implant100 can be reinforced by an embedded flexible fiber mesh, if desired, solong as the fiber mesh is not exposed on articulating surface 114, whichmust be kept extremely smooth and slippery. If desired, a portion of anysuch embedded mesh can extend outside of the peripheral rim 112, toprovide additional anchoring means. Alternately or additionally, strandsof anchoring material (such as suture strands, metal wires, flatpolymeric or metal eyelets, etc.) and/or one or more sheets or segmentsof flexible mesh or drape material, also can be affixed to the implant(such as at or near the anchoring screws), either during themanufacturing process, or by a surgeon immediately before or duringimplantation, to provide additional anchoring strength and stability.

It should be noted that placing a “non-homogenous” member inside apolymer component can sometimes weaken the overall strength of thepolymer component. Nevertheless, the types of reinforcing membersdisclosed herein can play highly valuable roles in achieving andproviding truly stable and durable anchoring systems. Accordingly, anyreferences to “reinforcing” components (or related phrases), as usedherein, are used to refer to embedded or attached components that canlead to either or both of the following results or effects:

(i) a stronger component or assembly, such as a complete implantassembly having a molded polymer component that is able to withstandhigher compressive, shearing, or other stresses and loads; and/or,

(ii) a stronger, more secure, and more durable anchoring attachment to ahard bone surface or other tissue.

For simplicity of illustration, the “underside” (or “anchoring surface”)116 of implant 100 is depicted as a smooth surface, in FIG. 3. In anactual implant, the anchoring surface (which normally will contact andpress against a prepared bone surface, from which damaged nativecartilage has been removed) preferably should have a fibrous, porous, orsimilar texture that will actively encourage the ingrowth of scar and/orbone tissue, to provide stronger and more stable anchoring of theimplant to a supporting bone surface (or other type of tissue, such asin the case of meniscal or labral implants). There are several knownways to create, in molded polymers, the type of porosity that willpromote cellular ingrowth. Alternately, the underside 115 of polymercomponent 110 can be bonded to an additional layer ofingrowth-and-anchoring material, such as a screen or mesh layer made ofseveral layers of very thin and flexible wires made of a titanium orother biocompatible alloy. In addition, any such anchoring surface canbe coated or impregnated with one or more hormones or growth factorsthat will accelerate the ingrowth of tissue into the anchoring surfaceof the implant, to promote faster recovery after the surgery.

In a preferred embodiment, a stabilizing ring 140 is embedded within theflexible polymeric component of peripheral rim 112. Ring 140 can also bereferred to by various other terms, such as an anchoring component oranchoring ring, or as a cable ring, cable anchor, anchor cable, orsimilar terms if it is made of a cable-type material. The term “cable”as used herein implies an elongated flexible component made from amulti-stranded material, which in most cases will be a flexible metal,or a synthetic polymeric material, such as “ultra-high molecular weightpolyethylene” (UHMWPE).

If desired, ring 140 can be made of a “shape-memory” or “super-elastic”material. Because a component which is fully embedded within a polymercomponent will not be contacted by body fluids in any appreciablequantity, a “nitinol”-type alloy can be used for this type of embeddedcomponent, if desired, despite the risks of gradual corrosion that canoccur over a span of years or decades when nitinol alloys are contactedby body fluids. Alternately, to alleviate potential regulatory concerns,and to render safety- and durability-testing easier, a shape-memory,super-elastic, or other polymer can be used to make stabilizing ring140; or, stabilizing ring 140 can alternately be made of a twisted orbraided multi-strand cable, as described below and illustrated in FIGS.7 and 8.

The type of implant assembly shown in FIGS. 1-8, containing a flexiblestabilizing ring 140 embedded within an enlarged flexible polymericcomponent around the peripheral outer rim 112 of an implant device, canallow a flexible surgical implant of this type to be bent, rolled, orotherwise flexed (without requiring tools, and with tolerable stressesthat will not cause any lasting damage to the implant) into acylindrical or compressed shape, for insertion into a joint via anarthroscopic insertion tube.

If the shape-memory and/or super-elastic stabilizing ring has atemperature-dependent behavior that causes it to become more flexibleand less rigid when it is chilled, then it can be chilled, immediatelybefore flexion and insertion, by a suitable step such as immersing it ina bowl of ice-cold saline slush. As the implant warms back up to bodytemperature, after it is inside the joint, the shape-memory stabilizingring will stiffen, imparting a reinforced final shape to the implant.

Alternately, if the stabilizing ring is made of a super-elastic materialthat does not require temperature manipulation to give it high levels offlexibility, then no such treatments are required, and other approachescan be considered. For example, if an elongated component made of asuper-elastic material has a half-circle or arc-shaped cross-section,similar to the cross-sectional shape of a tape measure, as depicted inthe stabilizing ring shown in FIG. 6, then it can offer substantialresistance to bending, but only up to a certain point (or level, extent,or similar terms) of flexion. When that point or level is reached, thearc-shaped cross-section will be forced and flattened into a linearcross-section, in a manner comparable to what happens to a metallic tapemeasure when it is retracted into a carrying case. After that type offlattening transitional deformation occurs, at one or more locationsaround the rim of an implant that is being flexed and rolled up, thestabilizing ring component can be bent with almost no resistance,thereby allowing an implant with this type of stabilizing ring to beinserted into a joint via an arthroscopic insertion tube. Once theimplant is inside the joint, it is allowed to relax and return to itsmanufactured size. When that occurs, the stabilizing ring will regainits original cross-sectional arc shape, and when that occurs, it willbecome much stiffer, in a way that will render it ideally suited forreinforcing, stiffening, and strengthening a cartilage-replacingimplant.

Regardless of which specific approach is used, a stabilizing ring madeof a shape-memory or super-elastic material can perform its reinforcingrole, once the rim of an implant with that type of embedded ring hasbeen properly positioned in a groove that has been machined (by thesurgeon, with the help of templates, computerized tool guides, etc.)into the bone surface that will support the implant.

In a preferred embodiment, stabilizing ring 140 can be provided withmeans for securing the implant to anchoring components, such as bonescrews. Alternately or additionally, the periphery of the implant can beprovided with other anchoring means, either directly or indirectly,which can be secured to bone or soft tissue by various known means,including staples, sutures, screws, etc.

In the embodiment illustrated in the drawings, three anchoring screws130 will be emplaced in the supporting bone, before the implant isinserted into the joint. This can be done with the aid of pilot holesthat will be drilled into a prepared bone surface (from which the nativecartilage has been removed), using a template or computerized guidingtool to establish the proper locations and angles of the screw holes andscrews. As shown in FIG. 4, the threads 132 of each bone screw 130 (onshaft 133) will have sizing and spacing suited for bone anchoring, andeach screw head 134 will have a rounded outer shape, to allow a “snapcap” 142 (affixed to stabilizing ring 140) to be secured to a screw, bysimply pressing snap cap 142 onto a screw head 134. Torsional drivingmeans (such as a hex socket 136, as shown in FIG. 4) should be providedon each screw head 134, to enable the surgeon to drive each screw 130into the bone, to a desired depth.

If desired, an enlarged “shoulder ring” 138 (or washer, or similarterms) can be provided around the “neck” of each bone screw 130. Theshoulder ring 138 can press directly against the bone surface ifdesired; alternately, it can settle into an accommodating washercomponent 139. If a washer component 139 is used, the bottom surface ofshoulder ring 138 preferably should have a beveled, angled, or roundedsurface, rather than a completely flat and planar disc-type rim, and the“seating surface” inside washer component 139 should have anaccommodating beveled or rounded surface. This will enable more stableand secure seating of the screw 130 in washer component 139, if a slightmisalignment occurs where a screw hole drilled into a bone surface isnot exactly perpendicular to the bone surface at that location.

As shown in greater detail in FIG. 5, each “snap cap” 142 can be securedto stabilizing ring 140, by any suitable means, such as a protruding tab(or finger, strap, or similar terms) that can be bent into a loopstructure 144 that will encircle ring 140. At each of the spacedattachment locations around the length of stabilizing ring 140, a“coupling detente” 146 can be provided. In this context, this type of“coupling detent” can refer to a localized bend, a drilled hole, awelded or crimped component, or any other device or component that willprevent sliding, slippage, or other displacement of the loop structures144 (or similar components) along the length of an anchoring rim 140,when those components are embedded within a polymer component.

In one preferred embodiment, coupling detentes 146 can consist of a“bend” that places the actual coupling location (i.e., the site whereloop 144, on a “snap cap” 142, wraps around anchoring rim 140) closer tothe surface of the bone that will support the implant. Coupling detentesthat have this arrangement can provide anchoring components that arepartially or fully “countersunk”, in a manner that allows the top of ascrew head, “snap cap”, or other anchoring structure to be “lower”(i.e., closer to and possibly aligned or “flush” with the bone surface),with less protrusion. This arrangement can reduce the risk that aprotrusion (or bump, hump, etc.) at the site of an anchoring componentmight either (i) damage the flexible polymer component of an implant, or(ii) create an unwanted irregularity in an otherwise flat orsmoothly-rounded articulating surface, after an implant has beeninstalled.

If desired, stabilizing ring 140 can be provided with a closure sleeve149 (illustrated in FIG. 2), to hold the two ends of a stabilizing ring140 together. If used, this type of closure sleeve 149 can be secured tothe two ends of a strand, cable, or other components, by means such ascrimping, a rivet, “snap rings” inside the sleeve 149, or similar means.In general, shape-memory and super-elastic materials are not well-suitedfor welding, and the types of stresses imposed on them often focus onany junctures or interfaces, in ways that often render glue or epoxyunreliable, and prone to failure. Therefore, other means of securing thetwo ends of a stabilizing ring, to each other, must be used, such as acrimped closure sleeve that tightly grips both ends of a ring.

Another configuration that merits evaluation would use a “key-ring”arrangement, in which the two ends of the stabilizing ring 140 overlapeach other, for some distance. Since both of the two ends will beembedded within a tough and durable polymer (if desired, a metallic orother sleeve can be tightly wrapped and/or crimped around at least aportion of any such overlap), this approach is likely to be useful in atleast some designs, especially non-circular designs. Any such juncturepreferably should be positioned, within any stabilizing ring in animplant as disclosed herein, in a location that will not be subjected tohigh flexure-related stresses, during the insertion stage of theoperation. For example, if a femoral runner implant has a shapecomparable to a ellipse or an oval-type racetrack, the juncture locationpreferably should be positioned near the middle of the most nearlystraight portion of the ring, rather than near the “apex” of a curvedportion of the ring.

Alternately, it is feasible and practical to provide a gap between thetwo ends of a stabilizer ring, if desired. Since the nature and purposeof the ring is simply to provide stabilization for the implant after theenlarged peripheral rim of an implant has settled into an accommodatinggroove or trench that has been machined into the surface of thesupporting bone, there is no specific need for the stabilizer ring toextend around the entire peripheral rim of an implant. For example, eachfemoral runner implant can be provided with an enlarged peripheral rimmade of molded polymer material, which will contain embedded stabilizersegments mainly located around the “curved ends” of the implant, whilethe two “side” portions (medial and lateral) of the implant peripherymight contain stabilizer segments that are long enough to provide secureanchoring attachments at or near all of the ends of the segments, butwhich do not comprise a complete “ring” that fully encircles andsurrounds the implant.

The molding and fabrication methods that will be required to make thesetypes of implants are well within the level of ordinary skill in thatfield of art. Any of various mechanical means can be used to suspend astabilizing ring at an appropriate height and position in a mold cavity,while a liquid “pre-polymer” is poured into the mold cavity, so that thestabilizing ring will be properly centered and embedded within theenlarged peripheral rim of the implant after the “pre-polymer” mixturehas set (or cured, hardened, polymerized, etc.) to form the flexiblepolymer. For example, if the stabilizing ring of an implant has “snapcaps” affixed to it, which are designed to be snapped onto the roundedheads of anchoring screws that have been emplaced in a supporting bone,then the molding cavity can include (or interact with) a device (oftencalled a “jig”) that will have the same number of rounded screw heads,positioned in the same spatial relationship with respect to the enlargedrim vacancy in the molding cavity.

Optimal designs for different types and sizes of implants, for differenttypes of joints and among different classes of patients, are likely tovary substantially. For example, finger and thumb joints are small, anddo not need to withstand nearly the loadings and stresses that areimposed on knee joints; accordingly, implants as disclosed herein forrepairing finger or thumb joints can rely entirely on suture strandsthat are wrapped around a peripheral anchoring cable, and that emergefrom the outer rim of the molded polymer component. By contrast, in mostpatients, implants for repairing a femoral runner or tibial implant, ina knee joint, will need to withstand much greater loads and stresses.Accordingly, any implants used for knee repairs normally should utilizea combination of bone screws and suture strands; however, even thatpresumption will need to be assessed, for each individual patient, by askilled orthopedic surgeon, depending on the status and needs of thepatient. For example, if a surgeon is treating an elderly woman who issuffering from serious osteoporosis and/or brittle bones, the surgeonmight decide that bone screws would pose an unacceptable risk ofdamaging that patient's already-fragile bones, so other anchoring meansshould be used instead of bone screws.

Accordingly, when such factors are taken into account, the designoptions that should be considered, for specific types and classes ofimplants, become somewhat broader, and the following factors should betaken into account.

For implants that will remain under relatively steady or low-levelcompressive loadings that do not need to withstand high shear stresses,such as in finger or thumb joints, relatively aggressive anchoringcomponents such as screws may not be required. Devices such as staples,sutures, and/or pins made of swellable materials (or using “spring-type”gripping mechanisms) can provide adequate alternatives for at least somesuch implants.

In addition, depending on the depth and shape of a groove or trench thatwill be machined into a bone surface to provide an accommodating“seating component” for the enlarged rim portion of an implant asdisclosed herein, it may be preferable in some cases to eliminateadditional anchoring components, and rely on a combination of otheranchoring meands, such as: (1) bone cement; (2) one or more suturestrands that are firmly secured to a flexible anchoring cable that isembedded within the polymeric rim of an implant; and/or, (3) “seating”of the enlarged rim component, within an accommodating groove, trench,or similar structure that has been machined into the supporting bonesurface. The level of security and stability that can be provided bythis approach can be enhanced by various methods or devices, such as by:(i) creating a bone groove that is angled slightly toward thecenterpoint of the implant, to create a “snap”-type fitting of theimplant rim into the bone groove; (ii) using a swellable material, aroughened outer surface, and/or similar means to create an implant rimthat will “grip” the bone groove more securely; (iii) using mechanicaltightening or cinching means, shape-memory components that will shrinkslightly when they warm up, or similar means to tighten the grip of therim on the interior wall or surface of the groove or trench in thesupporting bone surface; and, (iv) using other attachment means, includebone cement, which can bond to various types of polymers, and/or toother porous materials (such as wire meshes) that can be exposed on theanchoring surface of an implant.

In another preferred embodiment, a stabilizing ring can be provided withone or more segmented, protruding, or other components or surfaces(which can include eyelet devices, mesh materials, etc.) that willextend outside of the flexible polymer component of an implant. This canallow sutures, staples, bone cement, or other means to be used to securethe implant to the supporting bone.

In another preferred embodiment, a first anchoring component that doesnot contain a flexible polymer component can be securely affixed to aprepared bone surface, by means such as screws, staples, sutures, etc.To provide the surgeon with optimal working space, the initial anchoringsteps can be performed and completed before the flexible polymer implantdevice is inserted into the joint that is being repaired. After thatinitial anchoring procedure has been completed, the flexible polymerimplant can then be inserted into the joint, and either: (i) affixeddirectly to the first anchoring component; or, (ii) secured in place, ina manner that utilizes the anchoring component to provide greaterstrength and stability to the entire assembly.

This approach is illustrated in FIG. 6, which shows the same type ofimplant 100 as described above, having an enlarged rim 112 with astabilizing ring 141 made of a shape-memory material embedded within rim112. Stabilizing ring 141 has an arc-shaped cross-section, as describedbelow.

After the hyaline cartilage has been removed from a bone surface 90, andafter a groove 92 (sized and shaped to accommodate the rim 112 ofimplant 100) has been machined into the surface of the bone 90, asurgical implant that can be referred to as an “anchoring subassembly”160 is securely affixed to the surface of bone 90, along the inner edgeof the machined trench 92. Anchoring subassembly 160 comprises“trench-supplementing component” 162, which will effectively help “lockin” the enlarged rim component 112 of a flexible cartilage-replacingimplant. If desired, the trench-supplementing component 162 can be provided with an internal stabilizing ring 164, made of a shape-memory,super-elastic, or similar material, embedded within the ring-shapedtrench-supplementing component 162. The anchoring subassembly 160 can besecurely affixed to bone 90 with the aid of an anchoring disc 166, whichwill be secured to the bone by a plurality of anchoring means 168 (suchas screws, pins, staples, etc.). Anchoring disc 166 preferably should beprovided with the shape of an enlarged washer, having an open center;accordingly, it is referred to in the claims as a “washer component”.The open center will allow bone or scar tissue to grow directly into an“ingrowth surface” (as described above) on the anchoring side of theflexible polymeric implant.

The components shown in FIG. 6 are simplified, for purposes ofillustration; for example, to minimize any abrasion or damage to thepolymer component of an actual implant, anchoring screws or pins 168would be countersunk into the anchoring disc 166 or into the bonesurface, and the anchoring disc 166 can have a beveled, tapered, orrounded internal edge (alternately, it can be countersunk into a groovethat has been machined into the supporting bone, so that the upper edgeof anchoring disc 166 is flush with the prepared bone surface). Inaddition, while anchoring subassembly 160 as illustrated in FIG. 6 ispositioned in a manner that is partially nestled into the bone trench92, it alternately could be positioned outside the bone trench.

After the anchoring subassembly 160 has been fully anchored to the bone,a flexible polymeric implant (as shown in FIGS. 1-3) will be emplaceddirectly over it, and coupled to it (in FIG. 6, the flexible polymerdisc that spans the center portion of the implant is not shown, tosimplify the illustration of the anchoring mechanism). If desired, a“snap ring” type of securing mechanism can be used, since the tubularpolymer rim 112 that surrounds the stabilizer ring 141 will be flexible.Alternately, a partially-hydrated polymer, which will swell to a largersize when fully hydrated, can be used to form the implant rim 112. Ifdesired, bone cement or a bone-regenerating material can be used to helpensure that the implant rim 112 is firmly anchored within the groove 92that has been machined into the surface of bone 90.

Accordingly, FIG. 6 illustrates just one of various mechanical designsthat can utilize a combination of:

(i) an anchoring subassembly, which will be designed to be firmly andpermanently anchored directly to a prepared bone surface, while workingspace is available to do so (i.e., before the flexible polymer implantis inserted into the joint, via an insertion tube); and,

(ii) a flexible polymer component, which will be affixed to theanchoring subassembly in a manner which utilizes the already-affixedanchoring subassembly to provide a convenient and practical attachmentmechanism that will provide a strong and stable mounting system for theflexible polymer component.

In considering the techniques and devices that are disclosed herein, italso should be noted that the anchoring means that can be used for suchimplants can use combinations of: (i) permanent and nonresorbablecomponents, and (ii) resorbable sutures or other anchoring means, whichcan be designed to be gradually dissolved by bodily fluids while theingrowth of bone or scar tissue into a porous anchoring surface of theimplant provides permanent anchoring.

Stabilizing Rings with Variable Flexure Stiffness

In addition to the use of shape-memory materials to make the stabilizingrings disclosed herein, another design approach is disclosed herein,which utilizes controllable cross-sectional shapes to achieve (or atleast facilitate) the types of behaviors and performance results thatare desired for cartilage-replacing implants as disclosed herein.

This design approach can be better understood by considering thebehaviors of two common household items, which are: (1) inexpensiveplastic drinking straws; and, (2) metallic tape-measures.

When a standard plastic straw is bent slightly, it will exert some levelof resistance, only until it reaches a point where its circularcross-section is forced to collapse. When it reaches that transitionpoint (which can also be regarded as a failure point), it makes a rapidtransition to a flattened cross-section. Once that transition occurs,the straw can be bent easily, such as into a “hairpin” shape, where thecross-sectional shape of the straw, at the apex of the curve, will beeffectively flat.

A completely round and tubular straw will be damaged by that type ofbending, as can be seen by the ridges, wrinkles, or other deformationsthat will be created where the plastic material actually bent. Bycontrast, a conventional metallic tape-measure (of the type that isstored in rolled-up form inside a convenient case) suffers no suchdamage, since its cross-sectional shape is only a shallow arc, ratherthan a complete circle.

Using the conventional scales that are used to describe circles, thereare 360 degrees in a complete circle; an arc of 180 degrees is ahalf-circle; and, an arc of 90 degrees is a quarter-circle. Shortmetallic tape-measures (up to about 12 feet or 4 meters long) usuallyhave arcs of about 30 to 40 degrees, while longer tape measures (up toabout 25 feet or 8 meters) have arcs of about 80 degrees, to give themgreater stiffness when extended out to longer lengths.

Regardless of specific dimensions, any metal tape measure is designed toremain straight, and to resist bending forces, when in use and extended,thereby allowing it to be conveniently used to measure things whilesomeone holds the case in one hand, and uses the extended measuring tapein a manner similar to a pointing device. However, that type ofstiffness is effective only until the bending force reaches a transitionpoint, which will then force the tape to take a flattenedcross-sectional shape. If a tape has been extended beyond the distanceits “stiffness level” can support, it will suddenly bend somewhere alongits length, and the end of the tape will fall downward. Alternately,when a measuring task has been completed and the tape must be retractedback into the case, the tape will lose its arc shape and transform intoa flat layer along its entire length, as it is rolled up and retracted.Either type of transition is non-destructive; a metallic tape measure ofthis type will be made of a relatively elastic alloy that allows thetape measure to be extended (for use) and retracted (for storage) anunlimited number of times.

Accordingly, one preferred design for stabilizer rings as used hereincan utilize an arc-shaped cross-section (similar to the cross-sectionalarc of a tape measure), around at least a portion of a stabilizer ring.This design approach is illustrated in FIG. 6, in which the stabilizerring 141 has an arc shape, which in cross-section looks comparable to aparenthesis. As long as the entire ring 141 (and indeed the entireimplant 100) is in its original manufactured shape, when seen from aboveor below, stabilizer ring 141 will have a high or even very high degreeof stiffness. That is the shape and state it will return to, and remainin, once it is nestled and settled into an accommodating groove that hasbeen machined into a supporting bone surface. The stabilizing ring andthe groove will be designed to accommodate each other, withoutgenerating any stresses or deformation on stabilizing ring 141. In thatform, ring 141 can provide substantial stiffness, which is useful in astabilizing element.

However, during the insertion step, when the entire flexible implantmust be deformed in order to push it into the joint via an insertiontube, the stabilizing ring 141 can transform from its arc cross-section,into a flat cross-section that will allow almost unlimited bending, in amanner comparable to the way a metal tape-measure becomes flat at somelocation along its length, and thereafter allows virtually unlimitedbending with virtually no resistance, once it passes a transformational(i.e., flattening and collapse) point.

Use of Twisted or Braided Cables in Stabilizing Rings and Anchoring Rims

As mentioned above, if desired, a stabilizing ring (as shown in FIGS. 2and 5) or other anchoring rim component can be made of a cable,comprising twisted or braided wires or strands, as shown by cablecomponents 230 and 330 in FIGS. 7 and 8. If this approach is used, thecable will have an irregular surface, rather than the type of completelysmooth and relatively shiny surface that is found on extrudedsingle-strand wire. This will enable a polymer that is molded around ananchoring cable to strongly and securely grip the non-smooth surface ofthe cable, in a manner that will prevent any slipping, sliding, or otherdisplacement of the polymer along the length of the cable. This factorwill be reflected in a higher “pullout strength”, which is a testingfactor that indicates the amount of tensile force required to pull areinforcing or anchoring component out of a surrounding material.

The main components of implant 200, shown in a partial cutawayperspective view in FIG. 7, are:

(i) a flexible polymeric layer 210, which has a smooth and wettablearticulating surface 212, which will replace the articulating surface ofa segment of native cartilage that needs repair;

(ii) a porous layer 220, on anchoring surface 222. The anchoring surfacewill contact a prepared bone surface in an implant that replaces hyalinecartilage; alternately, it may contact either bone tissue or “capsulartissue” (which includes tendons, ligaments, membranes, or other softtissues) in a meniscal implant. The porous layer will promote tissueingrowth, for stronger and more stable long-term anchoring;

(iii) an anchoring cable 230, made of multiple moderately stiff but notrigid wires or strands 232, made of a metal alloy or suitable polymer orfiber; and,

(iv) a plurality of anchoring pegs 240 that have been provided withsuitable locking or affixing surfaces. In one preferred embodiment, asillustrated in FIG. 7, the locking surfaces can comprise a series of“sawtooth”-like ridges 242. Such ridges can either: (i) engage a set ofcorresponding ridges on the inside surfaces of anchoring sleeves, whichcan be emplaced in holes that have been drilled into a supporting bonesurface from which damaged cartilage has been removed; or, (ii) interactwith bone cement and with a drilled internal surface of a hole that hasbeen drilled into the bone, in a manner which can eliminate a need forusing anchoring sleeves embedded within a hole drilled into a bone.Alternately, if bone cement (rather than an anchoring sleeve) will beused, the ridged-type surface can be replaced by a different type oftextured surface that will provide better adhesion that can be obtainedwith a smooth and glossy surface.

In a large implant, such as to repair a knee or hip, a plurality ofanchoring pegs will be coupled to the anchoring cable 230, at suitablelocations around or near the outer rim of implant 200. In a smallimplant, such as a “button” implant for repairing a finger or thumbjoint, a single anchoring peg (or screw, as described below) can beused.

To simplify the drawing, no reinforcing mesh or other internal componentis shown within polymer layer 210 of implant 200, in FIG. 2. If desired,a reinforcing mesh made of strong fibers, a non-planar perforatedinterface between the polymer layer and the anchoring layer, and/or anyother internal component having a suitable size and shape can beembedded within the polymer layer of an implant of this type. It alsoshould be noted that an anchoring cable is not intended or used toreinforce the polymer component of a flexible implant, in a manner thatcan be accomplished by means of a reinforcing mesh, a non-planarperforated interface, or other type of reinforcing component that coversall or nearly all of the “area” (when seen in a “plan” view) of theimplant. Instead, the anchoring cable component 230 is intended for adifferent and distinct purpose, i.e., to provide the implant with acomponent that is located around its periphery, to provide stronger andmore secure anchoring of the entire implant device, to supporting boneand/or surrounding tissue.

Implant 300, shown in FIG. 8, also has a flexible polymeric layer 310with a smooth and wettable articulating surface 312. It normally willalso have a porous layer, to promote tissue ingrowth (which leads tobetter long-term strength and stability) on anchoring surface 320;however, as in FIG. 2, a porous anchoring layer is not shown in FIG. 8,to simplify the illustration. Anchoring cable 330 is shown as being madeof wires or strands 332, with ends that are held securely to each otherby a securing collar 334, which can be crimped, soldered, welded, orotherwise securely affixed to the two ends of the cable segment, therebyestablishing a continuous loop (or hoop, ring, etc.). Anchoring cable330 is embedded within an enlarged peripheral rim 340, made of theflexible polymer material.

The primary difference between implants 200 and 300 is that, instead ofusing anchoring pegs that will engage sleeves that must be set into abone surface, implant 300 uses “snap-cap” components 336, which can be“press-fit” (i.e., using compression, without requiring any rotation)onto the rounded heads of bone screws 350, which can be screwed intoholes drilled into a prepared bone surface. These types of “snap-cap”attachments can use multiple “fingers” (as shown), a constrainedinternal “split-ring” component, or similar devices made of a non-rigidalloy that imparts spring-like behavior to a cap, to allow it tosecurely grip and remain affixed to a rounded or other accommodatingscrew head.

Alternately or additionally, two other types of anchoring and securingdevices that are widely used and readily available in orthopedic surgerycan be adapted for use herein, to attach either or both of: (i) ananchoring cable that is embedded within the polymer component, or (ii)other components that will be used to secure the implant device, to boneor other tissue. One such class of devices is often called “fiberwires”, which are cables made of twisted or braided strands of“ultra-high molecular weight polyethylene” (UHMWPE), a polymer materialthat has greater strength than steel cables having the samecross-sectional dimensions. The second class of devices are called“cerclage wires”, which usually are made of titanium or stainless steelalloys; these commonly are used to help stabilize fractured bones, andthey frequently are used with small implantable devices that allow asurgeon to “lock down” and maintain a desired level of tension on anysuch wire, while it is being implanted. Either of these types of cablesor wires (or other comparable cables or wires) can be wrapped(preferably using several loops) around an anchoring cable as describedherein, prior to pouring a prepolymerized liquid into a mold that holdsthe anchoring cable. A flexible implant that results from this type ofmanufacturing process will have several strands of high-strength wire orcable, secured to the anchoring cable within the implant, with free endsthat emerging from the polymeric surface of implant. Those strands ofwire or cable (which can have eyelets, loops, or other devices at theirfree ends) can be used by a surgeon to anchor an implant, either bythemselves, or in conjunction with anchoring pegs or screws, or inconjunction with any other devices. In particular, such strands of wireor cable can pass through any of various types of “ratcheting anchors”,which are described and illustrated in more detail in parent applicationSer. No. 13/355,276, cited above. The contents of that application areincorporated herein by reference, as though fully set forth herein. Inparticular, that application discloses a new type of suture anchor withratcheting and locking capability, which is illustrated in FIGS. 9 and10, which are identical to FIGS. 10 and 11 in parent application Ser.No. 13/355,276.

Briefly, FIG. 9 shows ratcheting anchor 700 (with suture strand 750passing through it) prior to implantation in a bone surface, while FIG.10 shows the same ratcheting anchor 700 after it has been partiallydriven into a bone surface 699. Anchor device 700 comprises a generallycylndrical barrel portion 710, which has a tunnel or conduit 712 passingthrough it, and a generally conical pointed segment 730, which has atunnel or conduit 732 passing through it. The two main segments 710 and730 are coupled to each other by a relatively thin segment of deformablematerial at juncture 720, which is depicted as a circle in FIGS. 9 and10 for purposes of illustration, since it will provide a “pivot point”comparable to a hinge. Anchoring device 700 also is provided with a“crimping ramp” 740, which has a notched, ridged, sawtooth, or otherengaging surface 742, and a crimping corner or edge 744. As indicated inFIG. 10, the edge or corner 744 of crimping ramp 740 will press into andpinch the suture strand 750, in a manner which will effectively “lockdown” the suture at a fixed level of tension, after the surgeon exerts adesired final level of tension on the suture strand 750 and then bends(crimps) the anchor 700.

In most cases, when an implant is used to replace hyaline cartilage(i.e., the type of thin-layer cartilage that directly covers a condylarsurface of a bone), it will be anchored to a prepared bone surface fromwhich the native cartilage has been removed (by cutting, grinding, andother steps carried out by a surgeon). This approach, using directanchoring to a “freshened” bone surface (that term refers to a bonesurface that has been scraped, abraded, or otherwise treated to force itinto a “recovery mode”, which will promote tissue ingrowth into theporous anchoring surface of an layer), can provide a stronger, morestable, and more durable anchoring attachment, compared to laying animplant on top of diseased or injured cartilage that has not beenremoved from a bone condyle.

As briefly mentioned above, if an anchoring cable 230 or 330 is made ofa cable comprising twisted or braided wires or strands, it will have anirregular surface, rather than the type of completely smooth andrelatively shiny surface that is found on single-strand wire of the typethat is created by an extrusion process. This will enable a polymer thatis molded around an twisted or braided cable to strongly and securelygrip the non-smooth surface of the cable, in a manner that will preventany slipping, sliding, or other displacement of the polymer along thelength of the cable. This factor will be reflected in a higher “pulloutstrength”, which is a testing factor that indicates the amount oftensile force required to pull a reinforcing or anchoring component outof a surrounding material.

If a cable is used to provide a stabilizing ring or anchoring rim, itshould have a proper balance between stiffness, and flexibility (alsoreferred to by terms such as pliability). A complete implant assembly(which will include an anchoring cable embedded within a flexiblepolymer component) must be sufficiently pliable and flexible to allow itto be rolled up into a cylindrical configuration that can pass throughan arthroscopic insertion tube, during a surgical implantationprocedure. There is no fixed size limit for arthroscopic insertiontubes; nevertheless, the pressing and overriding goal of any suchoperation is to minimize the diameter of a tube that must be passedthrough the tissue that surrounds a joint, in order to minimize thedamage that must be inflicted on any tendons, ligaments, muscles, bloodvessels, or other soft tissues in the region that is being repaired.Accordingly, if a cable-anchored polymer implant has sufficientflexibility to allow it to be inserted into a joint via the smallest“practical” insertion tube, that flexibility can minimize: (i) thedamage that must be inflicted on surrounding tissues during surgery;(ii) the pain and recovery time that must be endured by the patient;(iii) the risk of infection, which will remain a threat until anyincisions have fully closed and healed; and, (iv) the risk of creating alasting unwanted post-repair condition what has been rendered suboptimalby unwanted scar tissue, improper tissue regeneration, infection, orsimilar factors.

However, after surgical insertion has been completed, a moderately stiffanchoring cable can help secure and stabilize an implant that willreplace a segment of hyaline cartilage that directly covers a hard bonesurface. This arises from the fact that an enlarged implant rim (such asrim 240, shown in FIG. 2) can be fitted and nestled into anaccommodating groove or trench that can be machined (with the aid oftemplates, computer-guided cutting tools, or similar devices) into ahard bone surface. If a jarring-type impact is caused by a jump, fall,accident, etc., or if a low level of stress in the implant or thesupporting bone is created by a non-optimal installation, any resultingstresses will be distributed and “smoothed out” over larger areas ofboth the bone and the implant, leading to higher levels of strength,durability, and resistance to wear, degradation, or damage.

By contrast, if a meniscal implant (or any other implant) is designed tobe affixed to tendons, ligaments, or other non-bone tissue, theanchoring cable generally should not be provided with high levels ofstiffness, and instead should be able to emulate and accommodate theflexibility of the surrounding soft tissue. In this type of arrangement,an anchoring cable made of thin and flexible fibers of a biocompatiblepolymer with high tensile strength is likely to be preferable to a cablemade of titanium or other metal alloy. In such a case, the function ofthe cable effectively will be to distribute and allocate any“point-loaded” stresses around a much larger area of the implant,thereby converting any localized “peak loadings” that might causeunacceptably high stresses, into low-level distributed stresses thatwill not cause any damage, even over a span of decades.

The proper balance between flexibility and stiffness, in an anchoringcable, will depend on the size, shape, and insertion site of an implant.As a simple illustration, an implant designed to replace a femoralrunner, in a knee, will have very different traits compared to animplant designed to repair a finger joint. To provide anchoring cablesthat can be positioned at any location along a very wide spectrum, with“extremely flexible” at one end and “extremely stiff” at the other endof the spectrum, three physical parameters can be modified andcontrolled, for any starting material, such as a titanium alloy or asuitable polymer. Those three physical traits are:

1. the thickness of each strand, which can range anywhere from (i) thinand fine wires (with diameters less than 0.1 mm) that can be readilybent, to (ii) thick and heavy wires (with diameters greater than 1 mm)that, when aggregated into a cable, can be bent only with the use oftools;

2. the number of strands that will be incorporated into a cable, whichin most cases will range between 3 (for relatively thick strands) andabout 20 (for relatively thin strands); and,

3. the looseness or tightness of the twisting or braiding structure, ina cable. If a cable with a twisted helical structure made of wirestrands is wrapped tightly (such as with several helical turns percentimeter of cable length), it will be stiffer than a cable that iswrapped loosely, within only a single turn (or a fraction of a turn) percentimeter of length.

By controlling those dimensional traits, a cable that is manufacturedfrom a particular type of suitable alloy or polymer can be given anydesired level of stiffness. Furthermore, a cable can be manufacturedfrom an assortment of strands having different diameters, and/or made ofdifferent materials. For example, a cable made with one, two, or threestrands of a relatively stiff metal alloy (such as stainless steel)having one or more chosen diameters, combined with a number of very thinstrands of a polymer having high tensile strength but low stiffness(such as conventional nylon fibers), can be created with any desiredlevel of stiffness.

Accordingly, a manufacturer can use these directly-controllable optionsand parameters to create an anchoring cable (either in a continuousloop, or in segments) that balances flexibility against stiffness at alevel that is optimized for any type of implant having a known size,shape, and intended site of implantation.

Flexible Cables for Anchoring Meniscal Implants

FIG. 11 depicts a meniscal implant 400, which has a shape that can bereferred to as an arc-shaped (or “arcuate”) wedge, somewhat similar to asection from a tangerine or other citrus fruit. Regardless of whether anative meniscal segment is on the interior or lateral side of a kneejoint, it will have three important surfaces, indicated in FIG. 9 as:

(i) an upper articulating surface 402, which will be smooth and“lubricious”, and which will press and articulate against the roundedbottom surface of a femoral runner

(ii) an outer peripheral surface 404, generally in the shape of avertical cylindrical segment, which will not articulate againstcartilage, and which instead will be coupled to the tissues which form a“knee capsule” (i.e., the tendons, ligaments, and membranes whichenclose and hold in the synovial fluid, which lubricates a knee joint);and,

(iii) a smooth and lubricious lower surface 406, which is roughlyplanar, and which rests upon and slides against an upper surface of atibial plateau. This lower surface is bounded and defined by a firstarcuate interior edge, a second arcuate peripheral edge, and opposingtips 408 and 409 where said first and second arcuate edges meet.

Accordingly, in one preferred embodiment, meniscal implant 400 isanchored, stabilized, and reinforced with the aid of two differentelongated flexible reinforcing members, which are depicted by “beadedlines” 422 and 432 in FIG. 9. Reinforcing member 422 is positioned alongor near the “lower” outer peripheral edge 420 of the meniscal wedge 400,and reinforcing member 432 is positioned along or near the “upper” outerperipheral edge 430 of the meniscal wedge 400.

For simplicity of illustration, both of the reinforcing members 422(lower) and 432 (upper) are depicted as extending out of and beyond thetwo opposing tips 408 and 409 of the flexible polymer material. Inactual practice, either or both of the lower and upper reinforcingmembers 422 and 432 are likely to be coupled, at each end, to aplug-type device that is coupled directly to (or positioned closelyadjacent to) the two tips 408 and 409 of the meniscal wedge. These typesof plug-type anchoring components can be set into small holes that havebeen drilled into a tibial plateau, in a manner that provides a larger,more distributed, and therefore stronger anchoring interface than can beachieved by a single screw or pin.

In addition, it likely will not be essential, in all cases, to providetwo different reinforcing members along both the lower and upperperipheral edges of a meniscus. For example, if the entire polymercomponent is reinforced by a fiber mesh, that mesh can eliminate theneed for a second elongated reinforcing member along the upperperipheral edge of the meniscal wedge.

Thus, there has been shown and described a new and useful design forsurgical implants for replacing and repairing cartilage. Although thisinvention has been exemplified for purposes of illustration anddescription by reference to certain specific embodiments, it will beapparent to those skilled in the art that various modifications,alterations, and equivalents of the illustrated examples are possible.Any such changes which derive directly from the teachings herein, andwhich do not depart from the spirit and scope of the invention, aredeemed to be covered by this invention.

1. A flexible implant for repairing damaged cartilage in a synovialjoint, comprising a flexible polymeric component having: (a) at leastone smooth and lubricious articulating surface; (b) at least oneanchoring surface that promotes tissue ingrowth; and, (c) at least oneperipheral anchoring edge which has an enlarged peripheral rim componentwith a size and shape designed to fit into an accommodating trench thathas been machined into a bone that will support the flexible implantafter implantation, wherein placement of said enlarged peripheral rimcomponent within an accommodating trench machined into a bone willprovide increased anchoring stability.
 2. The flexible implant of claim1, wherein said enlarged peripheral rim component contains at least oneelongated flexible reinforcing member embedded therein, and at least onetissue anchoring means coupled to said elongated flexible reinforcingmember.
 3. The flexible implant of claim 2 wherein said tissue anchoringmeans is selected from the group consisting of: a. a protrusion thatwill extend into a prepared hole in a bone surface; b. a component thatcan be secured to a head of a bone screw; c. one or more strands ofwire; d. one or more strands of suture material; e. a segment ofreinforcing mesh that is partially embedded within the flexible moldedpolymeric component and which extends out of said flexible moldedpolymeric component in at least one location; and, f. an eyelet devicewith an aperture.
 4. The flexible implant of claim 2 wherein saidelongated flexible reinforcing member embedded within said enlargedperipheral rim component is made of a material selected from the groupconsisting of: a. a shape-memory alloy having at least onetemperature-dependent physical or behavioral characteristic; b. ashape-memory polymer having at least one temperature-dependent physicalor behavioral characteristic; c. a super-elastic material; d. amulti-stranded cable; and, e. a high-strength polymer.
 5. The flexibleimplant of claim 1, wherein the implant can be flexed and deformed,without requiring tools and without suffering damage, into an elongatedshape having a width of about 75% or less of its relaxed width.
 6. Theflexible surgical implant of claim 1, wherein the implant can be flexedand deformed, without requiring tools and without suffering damage, intoa cylindrical arc wherein the opposed edges of the arc have an angulardisplacement of at least 70 degrees.
 7. The flexible surgical implant ofclaim 1, wherein the implant can be rolled into a cylindricalconfiguration and inserted into an articulating joint via anarthroscopic insertion tube.
 8. A flexible implant for repairing damagedhyaline or meniscal cartilage in an articulating mammalian joint,comprising a flexible molded polymeric component having: a. at least onesmooth and lubricious articulating surface; b. at least one peripheraledge which contains an elongated flexible reinforcing member embeddedtherein; and, c. a plurality of tissue anchoring components coupled tosaid elongated flexible reinforcing member.
 9. The flexible implant ofclaim 8 wherein said flexible implant is designed to replace hyalinecartilage and has a bone-anchoring surface that is entirely surroundedby a continuous peripheral edge, and wherein said elongated flexiblereinforcing member embedded within said continuous peripheral edge is asingle continuous reinforcing member that extends entirely around saidcontinuous peripheral edge.
 10. The flexible implant of claim 9 whereinat least a portion of said tissue anchoring components are selected fromthe group consisting of: a. protrusions that will extend into preparedholes in a bone surface; b. components that can be secured to a head ofa bone screw; c. strands of wire with ends that emerge from the flexiblemolded polymeric component; d. strands of suture material with ends thatemerge from the flexible molded polymeric component; e. a segment ofreinforcing mesh that is partially embedded within the flexible moldedpolymeric component and which extends out of said flexible moldedpolymeric component in at least one location; and, f. eyelet deviceswith apertures to accommodate shafts of screws or pins.
 11. The flexibleimplant of claim 9 wherein said elongated flexible reinforcing memberembedded within said peripheral edge is made of a material selected fromthe group consisting of: a. a shape-memory alloy having at least onetemperature-dependent physical or behavioral characteristic; b. ashape-memory polymer having at least one temperature-dependent physicalor behavioral characteristic; c. a super-elastic material; d. amulti-stranded cable.
 12. The flexible implant of claim 9, wherein theimplant can be flexed and deformed, without requiring tools and withoutsuffering damage, into an elongated shape having a width of about 75% orless of its relaxed width.
 13. The flexible surgical implant of claim 9,wherein the implant can be flexed and deformed, without requiring toolsand without suffering damage, into a cylindrical arc wherein the opposededges of the arc have an angular displacement of at least 70 degrees.14. The flexible surgical implant of claim 9, wherein the implant can berolled into a cylindrical configuration and inserted into anarticulating joint via an arthroscopic insertion tube.
 15. The flexibleimplant of claim 8 wherein said flexible implant is a flexible meniscalimplant, which is sized and shaped to replace meniscal cartilage, andwhich comprises a smooth and lubricious lower surface, which is sizedand shaped to articulate in contact with a tibial plateau, wherein saidlower surface is bounded and defined by a first arcuate interior edge, asecond arcuate peripheral edge, and opposing tips where said first andsecond arcuate edges meet, wherein said second arcuate peripheral edgehas at least one elongated flexible reinforcing member embedded therein,and wherein said elongated flexible reinforcing member has opposing endswhich are each coupled to an anchoring component.
 16. The flexiblemeniscal implant of claim 15, which also comprises: a. a smooth andlubricious upper articulating surface, sized and shaped to articulate incontact with a femoral runner, after implantation; b. an arcuateperipheral surface, sized and shaped to contact soft tissue in a kneecapsule, after implantation; and, c. an arcuate upper edge of saidflexible where said upper articulating surface and said arcuateperipheral surface meet; wherein an elongated flexible reinforcingmember is coupled to or embedded within said arcuate upper edge, andwherein a plurality of tissue anchoring components are coupled to saidelongated flexible reinforcing member.
 17. The flexible meniscal implantof claim 16, wherein said elongated flexible reinforcing member that iscoupled to or embedded within said arcuate upper edge has at least oneend which can be anchored directly to bone or soft tissue.
 18. Theflexible meniscal implant of claim 16, wherein said elongated flexiblereinforcing member that is coupled to or embedded within said arcuateupper edge has at least one end which is coupled to said elongatedflexible lower reinforcing member.
 19. The flexible meniscal implant ofclaim 16 wherein each of said lower and upper reinforcing members ismade of a material selected from the group consisting of: a. ashape-memory alloy having at least one temperature-dependent physical orbehavioral characteristic; b. a shape-memory polymer having at least onetemperature-dependent physical or behavioral characteristic; c. asuper-elastic material; d. a multi-stranded cable.
 20. The flexiblemeniscal implant of claim 16, wherein the implant can be flexed anddeformed, without requiring tools and without suffering damage, into anelongated shape having a width of about 75% or less of its relaxedwidth.
 21. A surgical implant for providing anchoring reinforcement fora cartilage-replacing implant, comprising: a. a washer component with anopen center area, wherein said washer component is sized to be securelyand permanently affixed to a bone surface, from which hyaline cartilagehas been removed, and which has been machined to create a trench whichwill accommodate a cartilage-replacing implant; and, b. atrench-supplementing component that is securely affixed to said washercomponent, and which is sized and positioned to provide a reinforcingstructure along an interior edge of a trench that has been machined intoa bone surface prior to emplacement of a cartilage-replacing implant.